[gtk+] Avoid a crash

[Matthias Clasen <matthiasc src gnome org>]

commit 3adb7c7a49938dd3d960957e1faa7e8e46193709
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Dec 22 14:08:03 2010 -0500

    Avoid a crash
    
    pointed out in bug 533745

 gdk/gdkdnd.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/gdk/gdkdnd.c b/gdk/gdkdnd.c
index 542f88f..bb2e6a8 100644
--- a/gdk/gdkdnd.c
+++ b/gdk/gdkdnd.c
@@ -451,6 +451,7 @@ GdkAtom
 gdk_drag_get_selection (GdkDragContext *context)
 {
   g_return_val_if_fail (GDK_IS_DRAG_CONTEXT (context), GDK_NONE);
+  g_return_val_if_fail (context->source_window != NULL, GDK_NONE);
 
   return GDK_DRAG_CONTEXT_GET_CLASS (context)->get_selection (context);
 }